Two problems which in the past have prevented the use of yeasts or bacteria as a food for human consumption are their high nucleic acid content and unacceptable palatability.
During metabolism in humans, nucleic acid breaks down to uric acid and therefore presents potential problems to human health, especially when large amounts are present in the blood stream. High uric acid content in blood is associated with diseases such as gout and tophi and with the formation of uric acid stones in the urinary tract. In order to use single-cell proteins such as yeasts and bacteria as a primary protein source for human population, the nucleic acid content obviously must be reduced to levels which are safe for human consumption. In this regard, a maximum level of nucleic acid intake is in the range of two grams of nucleic acid per day.
A procedure for degrading nucleic acids from unicellular organisms is through heat-shocking. (see e.g. R. D. Haight et al., Journal of Bacteriology, Nov. 1966, p. 1388). When an organism is placed in a thermal environment even slightly above its maximal growth temperature for any extended period of time, it soon dies and releases substantial portions of its nucleic acid. Unfortunately, this method is unsuitable for preparing high protein food products, since it simultaneously induces protein loss at a rate greater than or equal to loss of nucleic acids.
Ogata et al., in U.S. Pat. No. 3,139,385 disclose a method of producing nucleotides from living unicellular organisms by incubating them in an alkaline solution for 10 to 72 hours at a temperature of about 25.degree. to 30.degree. centigrade. Eighty to one-hundred percent of the intracellular nucleic acid disappears with this process, but the remaining product is not suitable for human consumption.
As set forth above, another problem associated with yeasts and bacteria as a protein source is their poor palatability. For example, yeast ordinarily has a sharp, pungent, salty taste. For this reason, if it is used as a protein supplement (in foods such as cereals, simulated milk, and grain), the natural flavor of the material to which the protein is added is substantially altered making the food undesirable or unpalatable.
Prior to the advent of the process disclosed in parent patent application Ser. No. 053,263, filed July 8, 1970, (now U.S. Pat. No. 3,720,585) entitled "Process for Reducing the Nucleic Acid Content in Yeast," the teachings of which are incorporated herein by reference, no truly acceptable method for reducing the nucleic acid content in yeast-like substances or bacteria were known which would simultaneously preserve their protein food value and enable the treated substance to be safely used as a palatable food source suitable for human consumption.
In addition to the specific yeast-like substances which are disclosed in U.S. Pat. No. 3,720,585 as being treatable by that process to render them edible, in accordance with the present invention, it has been discovered that bacteria such as the bacterium Bacillus subtillus and yeasts such as the strain of yeast known as Saccharomyces cerevisiae can be similarly treated to reduce the nucleic acid content thereof and produce a heretofore unknown food product.